Field Of The Invention
The present invention relates generally to electrochemical cells and systems, and more specifically to a dopant or other stabilizing agent that interacts with and/or protects the anode in the cell or system.
Description of Related Art
Certain metal additives can reduce hydrogen production or detrimental side reactions in electrochemical cells during storage or during their use to extend their charge retention time, shelf, or cycle life (see U.S. Pat. No. 3,639,176 and Huot et al., Electrochem. Soc. Proc., 95-14, pp. 22-26, 1996). One degradation mechanism for electrochemical cells can be the splitting of water or deterioration of the electrolyte and associated hydrogen generation. In primary zinc alkaline cells, it is known that anode alloys containing Hg or Pb can reduce hydrogen generation, for example from decomposition of water or other electrolyte components in the cell (see U.S. Pat. No. 6,652,676). This effect can be seen through studies of the hydrogen evolution exchange current versus the metal-to-hydride binding energy (Quaino et al., J. Nanotechnol. 2014, 5, 846-854).
FIG. 1 is a graph of hydrogen exchange current (in A/cm2) vs. hydride formation energy (in kcal/mol) in acidic solution. This graph shows the nature of metals such as Pb, Cd, Sn and Bi towards low hydrogen evolution, as compared to other metals such as Fe, Ir, Rh and Re.
Elements such as Hg and Pb have been alloyed into zinc anode materials to enhance charge retention, storage lifetimes and anode conductivity. Due to toxicity and environmental concerns, these elements were replaced with other elements such as Bi, Al and In. However, it can be difficult to source or produce these alloys in the appropriate particle size and/or with the desired alloy distribution (e.g., surface coating).
Corrosion of zinc can lead to self-discharge, shortened shelf life, reduced performance, cell gassing and other undesirable phenomena in an electrochemical cell. The key factors leading to zinc corrosion have been summarized into three main groups: 1) properties of the electrolyte, 2) properties of the zinc electrode and 3) operating conditions (X. Zhang, “Corrosion and Electrochemistry of Zinc,” Plenum/Springer, New York, N.Y., 1996). Some empirical studies have shown that the presence of certain inorganic species or compounds in the electrolyte or electrode can significantly decrease rate of zinc corrosion. These species or compounds have been added to an electrochemical system in known ways.
This “Description of the Background” section is provided for background information only. The statements in this “Description of the Background” section are not an admission that the subject matter disclosed in this section constitutes prior art to the present disclosure, and no part of this “Description of the Background” section may be used as an admission that any part of this application, including this section, constitutes prior art to the present disclosure.